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xdsl-smt

This repository contains a work-in-progress implementation of an SMTLib dialect for xDSL.

It currently contains the implementation of the core theory of SMTLib and a partial implementation of the bitvector theory.

It also contains a partial lowering from pdl, arith, comb, and func to smt, a translation validation tool between arith + comb + func programs.

Installation

Virtual environment

It is recommended to install the project in a virtual environment. To create a virtual environment, use the following commands:

# Create a virtual environment
python -m venv venv
# Activate the virtual environment
source venv/bin/activate

Installation

To install the project, use the following commands:

# Install the project
pip install .

Development installation

To setup an environment for hacking on xdsl-smt, use the following commands:

# Install the project in editable mode with dev dependencies
pip install -e '.[dev]'

Printing SMTLib

When a program only contains SMTLib operations and attributes, it can be printed as an SMTLib script with

xdsl-smt file.mlir -t smt

You can also directly run the SMTLib script with

xdsl-smt file.mlir -t smt | z3

or any other solver compatible with SMTLib.

Running the translation validation tool

The translation validator can be run with

xdsl-tv file_before.xdsl file_after.xdsl | z3

This command will check that the second program is a valid refinement of the first one.

In order to simplify debugging the refinement script, you can pass the -opt option to xdsl-tv to simplify obvious expressions and remove the use of the pair datatype.

Verifying PDL rewrites

PDL rewrites can be verified with the verify-pdl tool. It takes a single file as input, and will check for the correctness of all rewrites that are present in the file.

It is run with

verify-pdl file.mlir

Running passes with xdsl-smt

xdsl-smt uses the -p command to run passes on a program.

# Run dce, then convert arith to smt, and output the result in SMTLib form
xdsl-smt file.xdsl -p=dce,lower-to-smt,canonicalize,dce -t smt

xdsl-smt defines the following passes:

  • dce: Eliminate dead code.
  • canonicalize,dce: Apply simple peephole optimizations on SMT programs. This is useful for debugging generated code.
  • lower-pairs: Try to remove usage of pair datatypes. This duplicates function definitions when they return pairs.
  • lower-to-smt: Lowers arith, comb, func to the smt dialect. Can also be extended with additional rewrite patterns for new dialects.
  • pdl-to-smt: Lowers PDL rewrites to the smt dialect, using the lower-to-smt pass. The resulting SMT program will check that the rewrite is correct.

Extending the project with new semantics

The lowering to SMT can be extended with new semantics using the fields of the LowerToSMT class:

  • type_lowerers extends the lowering of types to SMT sorts.
  • rewrite_patterns extends the lowering of operations to SMT operations using rewrite patterns.
  • operation_semantics extends the lowering of operations to SMT operations using meta-level semantics. Giving semantics this way is necessary to support these operations in pdl-to-smt.
  • attribute_semantics extends the lowering of attributes to SMT attributes using meta-level semantics. Giving semantics this way is necessary to support these attributes in pdl-to-smt.

The lowering to SMT from PDL can additionally be extended with the following fields from PDLToSMT class:

  • native_rewrites extends the semantics of functions used in pdl.apply_native_rewrite
  • native_constraints extends the semantics of functions used in pdl.apply_native_constraint
  • native_static_constraints extends the semantics of function used in pdl.apply_native_constraint, when the constraint should be checked before the lowering to SMT. This can happen when a PDL rewrite yields an invalid SMT program when this constraint is not satisfied, for instance by creating non-verifying operations.